Device for measuring an activity of cadmium ions

ABSTRACT

A DEVICE FOR MEASURING AN ACTIVITY OF CADMIUM IONS COMPRISES A SELECTIVE ELECTRODE AND A REFERANCE ELECTRODE IMMERSED IN A SOLUTION CONTAINING CADMIUM IONS, SAID SELECTIVE ELECTRODE INCLUDING A DISC IN A BATCH COMPOSITION WHICH COMPPRISES A COMBINATION OF CADIUM CHALCOGENIDE AND AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF SILVER TELLURIED AND SILVER SELENIDE OR A COMBINATION   OF SILVER SULFIDE AND AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF CADMIUM TELLURIDE AND CADMIUM

June 26, 1973 KENJl HIGASHIYAMA ETAL 3,741,883

DEVICE FOR MEASURING AN ACTIVITY OF CADMIUM IONS Filed Feb. 28, 1972 United States Patent 3,741,883 DEVICE FOR MEASURING AN ACTIVITY OF CADMIUM IONS Kenji Higashiyama and Hiroshi Hirata, Katano, Japan, assignors to Matsushita Electric Industrial Co., Ltd., Osaka, Japan Filed Feb. 28, 1972, Ser. No. 229,813 Claims priority, application Japan, Mar. 2, 1971, 46/11,124, 46/11,125; Mar. 3, 1971, 46/11,408,

Int. Cl. G011! 27/30 U.S. Cl. 204195 M 6 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The invention relates to a device for measuring an activity of cadmium ions and more particularly to a device comprising a selective electrode responsive to the activity of cadmium ions and a reference electrode.

Cadmium ion activity can be determined by several methods such as chelatometric titration, spectrophotography and polarography. However, these methods generally require troublesome pretreatment for the sample before the measurement of cadmium ions.

It is desirable for chemical industry to have a device for measuring the activity of cadmium ions in a solution without any troublesome pretreatment similar to that of a pH glass electrode for measuring the pH value of a solution without any pretreatment of the solution to be tested.

An object of this invention is to provide a device for measuring directly the activity of cadmium ions in a solution.

A further object of this invention is to provide such a measuring device characterized by a high sensitivity to cadmium ions.

Another object of this invention is to provide a cadmium ion measuring device characterized by a high response to the cadmium ions.

These and other objects of this invention will be apparent upon consideration of the following detailed description taken together with accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a device for measuring cadmium ions in a solution in accordance with the invention; and

FIG. 2 is a cross sectional view of a disc for use in the device of FIG. 1.

A device for measuring an activity of cadmium ions according to the present invention comprises a selective electrode and a reference electrode immersed in a solution containing cadmium ions, whereby only another surface contacts with said solution. Said cadmium ion-selective electrode includes a disc which is in a batch composition comprising a combination of cadmium chalcogenide and at least one member selected from the group ice consisting of silver telluride and silver selenide, or in a batch composition comprising a combination of silver sulfide and at least one member selected from the group consisting of cadmium telluride and cadmium selenide. Said batch composition according to the present invention achieves a cadmium ion-selective electrode having a high sensitivity and a wide application range with pH value in a solution to be tested.

Referring to FIG. 1, reference character 10 designates, as a whole, a selective electrode which comprises a disc in a batch composition according to the present invention. Said lead 3 is enveloped by a sealed wire 4. A combination of said disc 1 and said lead 3 partly enveloped by said sealed wire 4 is enclosed in a housing 2 so that another surface of said disc 1 contacts with a solution 6. Said housing 2 is filled with an insulating resinous material 5. A reference electrode 7 partly immersed in said solution 6 is electrically connected to one terminal of a voltmeter 8 having a high impedance. Said lead 3 is electrically connected to another terminal of said voltmeter 8.

A variation in the logarithm of the activity of cadmium ions in said solution 6 has a substantially linear relation to the variation in the potential between said selective electrode 10 and said reference electrode 7, both being partly immersed in said solution 6. One can use any available and suitable electrode such as a saturated calomel electrode or a silver-silver chloride electrode as said reference electrode 7.

Said disc 1 is in a batch composition comprising a combination of 5-60 wt. percent of cadmium chalcogenide and 40-95 wt. percent of at least one member selected from the group consisting of silver telluride and silver selenide, or in a batch composition comprising of 40-95 wt. percent of silver sulfide and 5-60 wt. percent of at least one member selected from the group consisting of cadmium telluride and cadmium selenide in accordance with the invention.

A batch composition comprising a combination of more than 60 wt. percent of cadmium chalcogenide and less than 40 wt. percent of silver chalcogenide results in a low sensitivity of resultant electrode and in an unstable potential which is sensitive to the presence of static charges and visible light. A batch composition comprising a combination of less than 5 wt. percent of cadmium chalcogenide and more than 95 wt. percent of silver chalcogenide results in a low sensitivity and a long response time of resultant electrode.

Cadmium chalcogenide referred to herein is defined as cadmium sulfide, cadmium selenide and cadmium telluride.

A batch composition referred to herein is defined as a composition of starting materials before heating.

A better result is obtained by using a batch composition wherein said silver sulfide includes at least one member selected from the group consisting of silver selenide and silver telluride, the weight ratio of said silver sulfide to said one member being in a range from 1 to 10. This batch composition results in a high sensitivity, a short response time of resultant electrode.

A more preferable batch composition comprises a combination consisting essentially of 10 to 30 wt. percent of cadmium telluride and to wt. percent of silver sulfide.

A longer operation life can be obtained by providing said disc with a noble metal electrode such as gold, paladium or platinum electrode. Referring to FIG. 2, a disc 1 has a noble metal electrode 9 applied to one surface thereof. A lead 3 is electrically connected to said metal electrode 9 by any available and suitable method such as soldering. Said noble metal electrode 9 can be prepared by, for example, vacuum-depositing of a noble metal film or by applying an available commercially noble metal paint.

The disc for use in said selective electrode can be ob tained by heating a pressed body of a mixture of a given batch composition in accordance with a conventional ceramic method.

A mixture of starting materials of fine powder form in a given batch composition according to the present invention is mixed well in a dry method by any suitable and available equipment and is pressed into a disc in a desired form at a pressure of 100 to 20,000 kg./cm. The pressed disc is heated at a temperature of 100 to 600 C. for time period of l to hours preferably in a non-oxidizing atmosphere, such as nitrogen or argon.

The device according to the invention can be reliably used at temperatures from 0 to 95 C. The measured potential versus the logarithm of the activity of cadmium ions is substantially linear relation.

Many kinds of diverse ions such as sodium, potassium, calcium, magnesium, nickel, cobalt, aluminum, zinc, chloride, sulfate and perchlorate ions are tolerated and may coexist during the measurement of the activity of the cadmium ions. However, ferric, silver, mercuric, iodide and sulfide ions should be removed from the solution to be measured.

EXAMPLE 1 A mixture of 25 wt. percent of cadmium telluride and 75 wt. percent of silver sulfide is mixed well in a dry method and is pressed at a pressure of 10,000 kg./cm. into a disc mm. diameter and having a 3 mm. thickness. The pressed disc is heated at 400 C. for 2 hours in purified nitrogen gas stream having a flow rate of 0.2 l./min. The sintered disc is polished, at both surfaces, with silicon carbide abrasive and then with diamond paste into a thickne's sof 2 mm. The polished disc is provided, at one surface, with a gold electrode which is obtained from Du Pont gold paint #8115. The polished disc is connected, at the gold electrode, to a lead partly enveloped by a sealed wire and is mounted in a housing of polyvinyl chloride resin. The housing is filled with epoxy resin so as to build a selective electrode as shown in FIG. 1. A combination of the selective electrode and a saturated calomel electrode as a/reterence electrode is immersed in an aqueous solution of pure cadmium nitrate at 25 C. The potential between the selective electrode and the calomel electrode is measured by a voltmeter for use in a pH meter.

The device measures the activity of cadmium ions with a high sensitivity as shown in Table 1.

TABLE 1 A device for measuring the activity of cadmium ions is prepared in a manner similar to that of Example 1. A disc of Example 2 includes cadmium sulfide and silver telluride. The preparation of the disc is similar to that of Example 1. The potential between the selective electrode and the calomel electrode in the aqueous solution of pure cadmium nitrate is measured with the same procedure described in Example 1. The device measures the activity of cadmium ions with a high sensitivity as shown in Table 2.

TABLE 2 Potential, mv.

Activity of cadmium ions, M 1 1:99 1 5:95 1 25:75 1 60:50

1 Weight ratio of cadmium sulfide: silver telluride.

EXAMPLE 3 The device for measuring the activity of cadmium ions is prepared in similar manner to that of Example 1. A disc of Example 3 is in the composition of a mixture of the starting materials, cadmium selenide and silver sulfide. The preparation of the disc is similar to that of Example 1. The potential between the selective electrode and the saturated calomel electrode in an aqueous solu tion of pure cadmium nitrate is measured by the same procedure described in Example 1.

TABLE 3 Potential, mv.

Activity of cadmium ions, M 1 1:99 5195 l 25:76 1 50:50 1 60:40

l Weight ratio of cadmium selenide: silver selenide.

EXAMPLE 4 The device for measuring the activity of cadmium ions is prepared in similar manner to that of Example 1. A disc of Example 4 is in the composition of a mixture of the starting materials, cadmium telluride' and silver selenide. The preparation of the disc is similar to that of Example 1. The potential between the selective electrode and the saturated calomel electrode in an aqueous solution of pure cadmium nitrate is measured by the same procedure described in Example 1.

TABLE 4 Potential, mv. Activit of cadmium ions,M 1 1:99 5:95 26:75 50:50 60:40

1 Weight ratio of cadmium telluride: silver selenide EXAMPLE 5 The device for measuring the activity of cadmium ions is prepared in a similar manner to that of Example 1. A disc of Example 5 is in a composition of a mixture of the starting materials, cadmium selenide and silver selenide. The preparation of the disc is similar to that of Example 1. The potential between the selective electrode and the saturated calomel electrode in an aqueous solution of pure cadmium nitrate is measured by the same procedure discribed in Example 1.

1 Weight ratio of cadmium selenide: silver selenide A device for measuring the activity of cadmium ions is prepared in a manner similar to that of Example 1. A disc of Example 6 includes 25 wt. percent of cadmium telluride, 35 wt. percent of silver selenide and 40 wt. percent of silver sulfide. The preparation of the disc is similar to that of Example 1. The potential between the selective electrode and the saturated calomel electrode in an aqueous solution of pure cadmium nitrate is measured with the same procedure described in Example 1. The device measures the activity of cadmium ions with a high sensitivity as shown in Table 6.

A device for measuring the activity of cadmium ions is prepared in a manner similar to that of Example 1. A disc of Example 7 includes wt. percent of cadmium sulfide, 15 percent of cadmium telluride, 50 percent of silver sulfide and percent of silver selenide as the starting materials. The preparation of the disc is similar to that of Example 1. The potential between the selective electrode and the saturated calomel electrode in an aqueous solution of cadmium nitrate is measured with the same procedure described in Example 1. The device measures the activity of cadmium ions with a high sensitivity as shown in Table 7.

A device for measuring the activity of cadmium ions is prepared in a manner similar to that of Example 1; A disc of Example 8 includes 10 wt. percent of cadmium selenide, 15 percent of cadmium telluride and 75 percent of silver sulfide as the starting materials. The preparation of the disc is similar to that of Example 1. The potential between the selective electrode and the saturated calomel electrode in an aqueous solution of cadmium nitrate is measured with the same procedure described in Example 1.

TABLE 8 Activity of cadmium ions, M: Potential, mv. 10- 21 10 -48 1O 76 10- 106 10- 1 35 1O -l65 10 192 1O- 207 What is claimed is:

1. A device for measuring an activity of cadmium ions in solution comprising a selective electrode and a reference electrode, said selective electrode including a disc in a batch composition which comprises a combination of cadmium chalcogenide and at least one member selected from the group consisting of silver telluride and silver selenide, said disc having a lead connected to one surface thereof, the other surface thereof being adapted to be contacted by said solution.

2. A device for measuring an activity of cadmium ions as defined in claim 1, wherein said disc is in a batch composition comprising a combination of 5-60 wt. percent of cadmium chalcogenide and 40-95 wt. percent of at least one member selected from the group consisting of silver telluride and silver selenide.

3. A device for measuring an activity of cadmium ions in solution comprising a selective electrode and a reference electrode, said selective electrode including a disc in .a batch composition comprising a combination of silver sulfide and at least one member selected from the group consisting of cadmium telluride and cadmium selenide, said disc having a lead connected to one surface thereof, the other surface thereof being adapated to be contacted by said solution.

4. A device for measuring an activity of cadmium ions as defined in claim 3, wherein said disc is in a batch composition comprising a combination of 40-95 wt. percent of silver sulfide and 5-60 wt. percent of at least one member selected from the group consisting of cadmium telluride and cadmium selenide.

5. A device for measuring an activity of cadmium ions as defined in claim 4, wherein said disc additionally includes at least one member selected from the group consisting of silver telluride and silver selenide, the weight ratio of said silver sulfide to said one member being in a range from 1 to 10.

6. A device for measuring an activity of cadmium ions as defined in claim 3, wherein said combination consists essentially of 10 to 30 wt. percent of cadmium telluride and to wt. percent of silver sulfide.

References Cited UNITED STATES PATENTS 3,591,464 7/1971 Frant et a1 2041 T 3,669,862 6/1972 Hirata et a1. 204-195 M 3,672,962 6/ 1972 Frant et a1. 204---1 T GERALD L. KAPLAN, Primary Examiner 

